Linux Process Management Concepts: Difference between revisions

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* [[Linux#Concepts|Linux]]
* [[Linux#Concepts|Linux]]
=Process=
The process with ID 0 is the swapper (or sched), the process responsible with paging. It is part of the kernel, rather than user-space.
<span id="The_init_Process"></span>The process with ID 1 is the init process, and it is responsible with starting and shutting down the system.
=Threads=
The number of threads for process can be read from the process' corresponding /proc/<pid>/status, as described here: [[Linux_Process_Information#Threads|"Threads:"]].


=Maximum Number of Processes Allowed on the System=
=Maximum Number of Processes Allowed on the System=
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cat /proc/sys/kernel/pid_max
cat /proc/sys/kernel/pid_max
</pre>
</pre>
or
<pre>
sysctl kernel.pid_max
</pre>
For more details, see [[sysctl]] and [[Kernel_Runtime_Configuration#kernel.pid_max|kernel.pid_max]].
To get the actual number of processes present in the system, see <tt>[[Linux_Process_Information#.2Fproc.2Fstat|/proc/stat]]</tt>.


=Maximum Number of Processes Available to a Single User=
=Maximum Number of Processes Available to a Single User=


The current value can be read and set with [[Ulimit#Options|ulimit -u]].
The current value can be read and set with [[Ulimit#Options|ulimit -u]].
For Java applications, this setting limits the number of threads a JVM can create, and it can cause the JVM to throw "java.lang.OutOfMemoryError: unable to create new native thread" exceptions when that limit is reached. For more details see {{Internal|Java_Threads#Java_Threads_and_Linux_Processes|Java Threads and Linux Processes}}
The O/S level symptom of reaching the per-user process limit is:
<pre>
-bash: fork: retry: Resource temporarily unavailable
</pre>
while trying to execute an arbitrary process.

Latest revision as of 01:26, 16 July 2017

Internal

Process

The process with ID 0 is the swapper (or sched), the process responsible with paging. It is part of the kernel, rather than user-space.

The process with ID 1 is the init process, and it is responsible with starting and shutting down the system.

Threads

The number of threads for process can be read from the process' corresponding /proc/<pid>/status, as described here: "Threads:".

Maximum Number of Processes Allowed on the System

cat /proc/sys/kernel/pid_max

or

sysctl kernel.pid_max

For more details, see sysctl and kernel.pid_max.

To get the actual number of processes present in the system, see /proc/stat.

Maximum Number of Processes Available to a Single User

The current value can be read and set with ulimit -u.

For Java applications, this setting limits the number of threads a JVM can create, and it can cause the JVM to throw "java.lang.OutOfMemoryError: unable to create new native thread" exceptions when that limit is reached. For more details see

Java Threads and Linux Processes

The O/S level symptom of reaching the per-user process limit is:

-bash: fork: retry: Resource temporarily unavailable

while trying to execute an arbitrary process.